texts: Opening VLA Export Format data on Windows

texts:
I recently downloaded some data from the NRAO archive.
It came as a file in the "VLA export format" with the extension .xp1. From what I gather I can open this using some software called CASA or a Python library called casatools using the importvla command.
The trouble is that I can't seem to find any way to install CASA on Windows 10. Infact as far as I can tell CASA isn't supported at all for Windows.
How do I open this file on Windows? I just want a big matrix of data that I can process with my own tools and astropy. Is there some reason that the NRAO distributes data using this (as far as I can tell) arcane and undocumented (I couldn't find any documentation after about 1/2 an hour of looking) file format instead of something like NetCDF or hdf5?


texts: Theoretical sudden appearance of a black hole in BBC drama show *spoiler warning*

texts:
I asked this on the ‘movies’ stackexchange site but they suggested I ask here, it’s a purely hypothetical query based on a BBC drama show called ‘Hard Sun’, feel free to kill the question if it’s inappropriate here.

In the TV show’s series finale an expected ‘extinction level event’ happens and appears to be a black hole close to our sun, it already has developed a spiral of hot gas around it drawn from the sun.

Clearly this is fiction but I’m keen to understand just how badly-considered this is. Firstly the show is set in London and everyone seems amazed when the image below rises from the dusk yet clearly it's been in existence for the time taken to create the spiral (hours at least?) so nations east of the UK would have seen it for that time and reported on it globally surely?

My real question is more around is there any potential scenario where a black hole of that size could develop suddenly and get to that size quickly enough for that image to be a surprise? My understanding, very much as a scientific-layman, is that a black hole of that size would have to have the mass of at least one of our suns to get to that size (probably more) - is that a valid assumption? If so where has the mass come from? Also wouldn't the sudden existence of something else with at least the same mass as our sun suddenly appearing at the centre of our solar system have enormous gravitational impact on everything in the system, including Earth? We'd have massive volcanic/tectonic impact wouldn't we?

So again sorry if this is inappropriate, I was just incredulous at how badly-considered the scientific aspects of this fiction were and wanted to check that my understandings were correct.

Screengrab:


texts: Question regarding the Milky Way when calculating galactic space velocities for galaxies

texts:
I have been calculating galaxy space velocities (where proper motions are known) in order to measure their orbits of the Milky Way using the method proposed in the appendix of http://www.aanda.org/articles/aa/pdf/2011/01/aa13415-09.pdf

The question I have is: Do we put the Milky Way through the same calculation process to get an initial velocity, or do we have that it's (0,0,0) as it is essentially our origin point (ie the U velocity component would mean that the Milky Way is moving in the direction away from its own galactic centre which doesn't really make sense to me as this could be any direction)?

I have put it through the process and found an initial space velocity of the Milky Way of (-11.1,232.24,7.25) (my method differs slightly from the link since I have used an updated velocity vector for the motion of the sun with respect to the Local standard of Rest) which essentially just comes from correction solar and galaxy rotation motions.

So, is this calculated vector correct for the Milky Way or should it be (0,0,0)?

Thanks


texts: Latitude, longitude and altitude of Ckoirama Observatory; where can things like this be looked-up?

texts:
This answer to Is Starlink 1130 (Darksat) really dimmer? links to the March 16, 2020 paper in arXiv First observations and magnitude measurement of SpaceX's Darksat which finds only a modest decrease in brightness:

  Results. The calibration, image processing and analysis of the Darksat Sloan g’ image gives an estimated Sloan g’ magnitude of 7.57±0.04 at a range of 976.50 km. For STARLINK-1113 an estimated Sloan g’ magnitude of 6.69±0.05 at a range of 941.62 km was found. When scaled to a range of 550 km, a reduction of (55 % ± 4.8 %) is seen in the reflected solar flux between Darksat and STARLINK-1113.

The v1 preprint says

  ...using the longitude(24.1° west) and latitude (69.9°south) of the Ckoirama observatory...

which puts the Ckoirama observatory under about 4500 meters of freezing antarctic water (first image).

If I invert the latitude and longitude assignments it returns to the Atacama desert where it belongs. If I instead type "Ckoirama observatory" in maps.google.com I get a pin on a map near 24.0894 S, 69.9305 W but the satellite image only shows a hole in the ground. (second image)

click images for full size

The sidebar says:

Antofagasta, Chile W369+6Q Yungay, Antofagasta, Chile
astro.uantof.cl
+56 55 263 xxxx
Open now:  Open 24 hours

That link leads to http://www.astro.uantof.cl/research/observatorios/ckoirama-observatory/ which is very informative but has no latitude, longitude or altitude information. 5 Awesome Observatories Around The World mentions that Ckoirama is;

  the first observatory built by Chilean engineers

and links to Astrotourism in Chile but no specific information.

Question: What are the latitude, longitude and altitude of Ckoirama observatory? Is there a central location where coordinates like these can be looked up?


texts:
Problem: Suppose an observer's latitude is 45 S and a star's RA/DEC is
3h15min/41S. On what date will the sun set with the star.

I have been stuck on this problem for a while.
I found out that the time of setting of a star is found using the formula:

$$\alpha+\arccos(-\tan(\delta).\tan(\phi))$$
$\implies3\frac{1}{4}^h+\arccos(-\tan(-41)\tan(-45)) = \alpha_{sun}+\arccos(-\tan(\delta_{sun})\tan(-45))$
$\implies 47.8 = \alpha_{sun}+arccos(tan(\delta_{sun}))$

I am not able to solve this any further.
Is there something wrong in my approach? Something I am missing?
If not how do I solve the above equation further?
Thanks in anticipation!


texts: The Kirkwood gaps in the asteroid belt are associated with orbital resonances with Jupiter yet planets seem to prefer resonant locations. Why don't asteroids accumulate near the "Kirkwood locations" rather than avoid them??


texts: Explanation for the mathematics behind Venus' retrograde motion

texts:
I've always been interested by the pattern within Venus' orbit around the sun. I found this image and formula of its retrograde motion in the upper right hand corner which confused me. What does it mean? can someone break this down in layman's terms?

Thank you


texts: Hot and "warm" Jupiters expelling terrestrial planets?

texts:
I've seen in documentaries that if a Jupiter size planet migrates close to its star then it would remove terrestrial planets along the way. This makes sense and I'm sure most models would predict this, but do we have evidence?

Indeed, the Kepler survey (taking Kepler 1-447) found 34 Planets>6 R(Earth) less than 0.1 AU from the star and the only one where another planet was found was Kepler 424 which also has a Jupiter size planet at 0.73 AU. Three "warm" Jupiters (0.1- 1.7AU) out of 47 have earth-size planets discovered in same system and all are "mini-solar systems" with the smaller planets far interior. (K68,90 and 407). If you include "super-earths" (R = 1.25-2.0 R(Earth)), then there are 7 additional stars found with "warm Jupiters" in multiple systems. The super-earths are still all inside the Jupiter's (although K18,89 and 118 have Jupiters less than 0.2 AU).

  My question is:

  Is this finding proof that migrating Jupiters have thrown out
  terrestrial planets or do their existence make the signals of
  "exterior" planets hard to discern? And what about smaller planets
  migrating in "behind" the Jupiter's?


texts: What is the size of the image sensor in the largest optical telescopes?

texts:
What image sensors (imaging electronics) are used in telescopes? Like CCD, is that the best option?
What is the typical physical size and resolution of the photo-sensitive surface of the currently active largest ones?


texts: What are the maximum and minimum impact speeds for an asteroid that would strike the Earth?

texts:
I gather that the impact speed depends on the radius of the orbit of the asteroid.

Is the orbit of asteroids in the same direction around the sun, or can they move in the "opposite" direction?


texts: When were the horizontal and equatorial celestial coordinate systems invented?

texts: When were the Alt-az system and the RA-dec system first used?


texts: Could a closely orbiting pulsar be used to study a black hole?

texts: If we were to locate a pulsar in a close elliptical orbit around a black hole, could this reveal significant information about the black hole (e.g. time dilation / structure)?  Could this even tell us the structure of a black hole (e.g. if it is a singularity, or a sphere formed around the event horizon, or something else)?


texts: Frequency of transit in planar and non-planar planetary systems

texts:
Supposing that another planetary system is in one plane like our solar system, if let's say that the transit of one planet is visible then is it safe to also assume that all planets in the system must transit?

Logically I feel like that this makes sense because since they are all in the same plane then they therefore must all transit as well. But then I feel like the transit probability equation could make this false? Could someone please clarify my doubts?

Also suppose that we are in another system where each planet doesn't necessarily orbit in the same plane.  Is it easier to find transits if the planets are orbiting in the same or random planes?

I think that you have a better chance detecting a planet if they are in random orbits. but i am a bit lost in regards to detecting multiple transits.


texts: Orbital Mechanics: where can I find initial conditions for orientations and angular rates of planets in our solar system?

texts:
I am looking to write the equations of motion (EOMs) for a 6DOF analysis of our solar system.  I want to integrate the equations forward in time, and need a complete set of initial conditions to do so. I'd like to fix a coordinate system on the center of the Sun for this simulation.
It appears that I can get the cartesian vectors (position and velocities) for the planets from HORIZONS
But what I am having trouble with is getting initial conditions for the orientations and angular rates of the planets. In my mechanical engineering mind, I'd like to ultimately get some angles and rates that I can relate back to Euler angles (and their rates) and work from there.
Angles:
I could set the initial rotation angle to zero, I'm sure that would be fine, but the other two don't seem to be as clear.
For example, on Horizons, it appears that I can find obliquity, which (correct me if I am wrong) is the angle between the orbital plane and the sun.  But I would need one more angle to specify the orientation of the rotation axis, correct?
Angular Rates:
Rotation rate is given by horizons - so I can work with that.  But what about precession and nutation?
I also see that obliquity changes over time - which implies that there should be some initial obliquity rate of change - how do these all relate?


texts: how far away can close stars diverge with time?

texts:
Do high velocity stars decelerate if they transit at 300ly per million years? What kind of forces can decelerate them and in what kind of time frame?

What about ordinary stars which travel at 70 light years per million, i.e alpha centauri? How often do they change direction and do they end 1000ds of light years away after a billion years?


texts: Is it be correct to say that we live in a young (only 14 billion years old) universe?

texts:
From what I have read, it seems that our universe is expected to function more or less as it does now for some $10^{12}$ years, possibly more. If that is correct, our universe's current age of $14$ billion years seems like this place we live in is still a baby, or at most a child.

I realize we are a long way from being sure about making such a broad characterization. Nevertheless, does it generally accord with current astronomical and cosmological thinking to say that our universe is still young?


texts: What complementary observation campaigns have looked at Kepler's field of view?

texts:
It seems to be common practice to double up observations. For example, shortly before New Horizons flew by Pluto, several of its moons were discovered by telescopes as a concerted effort was put in because of the occasion.

Have other telescopes made systematic and dedicated observations of the field of view of the Kepler telescope? I imagine speculatively in this paragraph that such observations could've been part of a survey process to determine where to point Kepler out of a set of candidate FOVs to begin with. And once decided upon, that field more closely examined. Then during the Kepler mission persistently observed in order to help rule out noise from passing asteroids and binary and variable stars and to gather complementary data. To characterize transiting planets, it is important to characterize the stars they are orbiting, something which telescopes with other kinds of instruments can be helpful with. Those are just my speculations about why I would think that Kepler's primary mission was "doubled up" by other kinds of telescopes.

What are some of the preparatory, complementary or follow up observation campaigns that have been made of the Kepler field of view? Is Kepler's FOV now one of the most and best observed parts of the sky?


texts: If a pulsar's rotational and magnetic axes were aligned and both aimed at us, would we see a steady radio source?


texts: How did the Mars satellites "take cover" from the recent comet flyby?

texts:
After comet Sliding Spring's Oct. 19, 2014 close flyby of Mars, NASA reports that

  All three NASA orbiters around Mars confirmed their healthy status Sunday after each took shelter behind Mars during a period of risk from dust [from the comet's tail].

"Took shelter behind Mars"?  These spacecraft are in orbit around Mars, constantly in motion, so they can't very well just pack up and move to the other side of Mars to avoid getting hit with the dust.

So my questions are: What exactly qualifies as taking shelter behind Mars?  Does it simply mean being on the other side of the planet from the tail of the comet as dust from the tail passed Mars?

How did NASA get the (constantly in motion) spacecraft to hide behind Mars?  I assume that the orbits had to be modified in advance of the comet's arrival. I picture some orbital modifications that changed the phase of the orbits of the satellites so that they would be on the other side of Mars as the dust flew by, perhaps also making the orbits more elliptical with the apsis behind Mars, allowing the satellites to spend additional time in Mars' protection.

Will these orbital modifications affect the ability of the spacecraft to fulfil their primary missions as they relate to Mars?  I am not asking whether dust from the comet will affect the quality of the instruments on the spacecraft (indeed, this whole question focuses on steps NASA is taking to prevent that from happening) but whether the altered orbits the spacecraft have after their orbital modifications will affect their ability to pursue their primary missions (such as flying over different parts of Mars than was originally intended, which may or may not be beneficial to answering the questions the spacecraft were originally launched to answer.  Although scientists are nothing if not resourceful and I'm sure any data that come from the spacecraft, whether intended or not, will lead to important discoveries).


texts: Why the lows of the GRB 2014-04-27 in Andromeda?

texts:
The Swift gamma ray burst space telescope has measured a GRB according to the link below. But why the oscillations in the measured gamma rate? Why wasn't just an increase detected, but also as big decreases? The average rate doesn't look to have increased during the burst. If averaged out over a minute the line would've been flat. Is there a fundamental astronomical explanation or has it to do with the technicalities of the instrument?
http://www.universetoday.com/112194/possible-gamma-ray-burst-detected-in-andromeda-would-be-closest-ever-observed/


texts: If a star that has regular pulses(standard candle) is flying away from us at relativistic velocity(very distant), would that pulses look like very sluggish compared to a non-relativistic velocity(close to earth)...something like a clock ticking in a relativistic spaceship and....... ofcourse red-shifted.Thanks.


texts: What are the problems that need to be taken in consideration when trying to find planetary position by using jpl ephemerides?

texts:
I'm currently trying to determine the position of the sun and the moon from jpl ephemeris DE200 which is referred to the dynamical equator and equinox of 2000 and uses tdb time. I am using the j2000  system ECI.The things that trouble me are the following:

1.Is the moon position given with respect to Earth or with respect to the barycenter? Also when we find the sun position by using the earth-moon barycenter position and lunar coordinate , will the sun position be with respect to Earth?

2.If I'm using UTC time  , how exactly to obtain the TDB or TAi, since it's oscillating?( After that I want to obtain the JD for TDB)

3.If I'm using  J2000 ECI coordinate system , do I need to take in acount the effect of nutation and precession? And how to do that?


texts: Difference between zone time and local sidereal time?

texts:
What is the key difference between LST and ZT?
Also, are UT, GMT and Greenwich Mean Solar Time the same?


texts: Are red dwarfs really 30-100 times our Sun's density?

texts:
This article by K. E. Edgeworth claims red dwarfs tend to be around 30-100 times our Sun's density.  However, this seems a bit high.
With smaller stars, mass tends to be proportional to radius but have a notably smaller volume, leading to higher densities.  This Wikipedia article labels red dwarfs as massing between 0.08 and 0.45 solar masses.
However, following mass being proportional to radius, a 0.25 solar radii star with 0.25 solar masses has a density of 22.5003 g/cm³, or about 16 times our Sun's density.
A star 1/4 the size and mass of ours is smack in the middle of the red dwarf range, but is only about halfway to the 30 times our Sun's density minimum the above article outlines, while based on the above article I would expect a red dwarf 1/4 the size and mass as our Sun to have a density more like 60 times our Sun's.
What is the cause of this discrepancy?


texts: What are the most valuable meteorites and asteroids in terms of precious metals?

texts:
There were some suggestions that asteroids could one day be mined for precious metals. I have found an outdated study that says that some siderites contain as much as 0.001% of gold:
http://pubs.usgs.gov/circ/1968/0603/report.pdf

Are there recent studies on precious metals in space rocks, i.e. platinum, rhodium, iridium, rhenium, osmium, ruthenium, palladium, germanium and gold, and is it genuinely a viable mining research subject?


texts: What is the equilibrium temperature that a black body will reach at the Earth's distance from Sun?


texts:
Please forgive my ignorance. I dare say that these questions arise from me trying to understand the nature of the Universe using Newtonian physics. There are a few things that really bother me when topics such as red shift and expansion are discussed.

1) We can view a Galaxy that is 30bn light years away because the light we are seeing it as it was 13bn years ago, and at that time it was only 13bn light years away. So, it has travelled 17bn years further in the last 13bn years? Faster than the speed of light?

2) 13bn years ago, it was 13bn light years away. That is around the time of the big bang. How did it manage to get that far away so soon after the Universe began.

3) How is the known Universe even as big as 40bn light years, after only 13bn years in existence.


texts: What's special about Saturn that it has distinctive rings?

texts: This may overlap with other questions, but I'm asking what is unique about Saturn in location, properties, etc that is has far more pronounced rings?   It's between Jupiter and Uranus and Neptune in size and position.  So what's special?  Is there some Goldilocks zone of rings formation?   Or is it just an accident of history?


texts: How to calculate Longitude from Right Ascension?

texts:
Considering that a star of certain declination is crossing the local meridian at the observer's zenith at an unknown location on the earth. Here, the declination of the star is equal to the observer's latitude. Knowing the Right Ascension of the star, how could the observer calculate his longitude?

Example: The star Miaplacidus (Dec: -69° 42' and RA: 9h 13m) crossing at the observer's zenith!

Latitude = 69° 42' S

[ Longitude= RA(Decimal Conversion) X 15° ... I'm not sure how to proceed from here ... ]


texts: What is the official classification and naming system of objects in the universe(, or what would my URI look like)?

texts:
Poetic human centric approach:

Universe/Laniakea/Virgo/MilkyWay/Sol/Earth/Humans/AndreasT

Little bit more technical:

Universe/0/SuperCluster/0/GalaxyCluster/0/Galaxy/0/StarCluster/0/Star/0/Planet/3/../HomoSapiensSapiens/2834929849289

More ... multiversal?

Or is there something in the spirit of the rebasing of SI units to universal concepts that makes us not be the origin(hah!) of the system?


texts: Why does the author believe that the central mass that gas cloud HCN-0.009-0.044 orbits is smaller than our solar system?

texts:
Phys.org's Hiding black hole found says:

A research team led by Shunya Takekawa at the National Astronomical Observatory of Japan noticed HCN-0.009-0.044, a gas cloud moving strangely near the center of the galaxy 25,000 light-years away from Earth in the constellation Sagittarius. They used ALMA (Atacama Large Millimeter/submillimeter Array) to perform high-resolution observations of the cloud and found that it is swirling around a massive invisible object.
Takekawa says, "Detailed kinematic analyses revealed that an enormous mass, 30,000 times that of the sun, was concentrated in a region much smaller than our solar system. This and the lack of any observed object at that location strongly suggests an intermediate-mass black hole. By analyzing other anomalous clouds, we hope to expose other quiet black holes."

The paper is Indication of Another Intermediate-mass Black Hole in the Galactic Center and is open access.
The quote in the second paragraph is all over the internet. I have found that sciencedaily and iflscience both link back to the same quote on an official NAO page here.

Takekawa explains, “Detailed kinematic analyses revealed that an enormous mass, 30,000 times that of the Sun, was concentrated in a region much smaller than our Solar System.”

Questions: How do they know that the central mass is "concentrated in a region much smaller than our Solar System"?
This answer about the paper and subsequent discussions below it don't seem to shed any light on this particular question. The NAO page does not indicate the origin of the quote, I'm wondering if it is a translation of a corresponding Japanese language page on the same site that explains further.


texts:
I am searching for a simple, modern catalog of Active Galactic Nuclei. I expected a catalog similar to this or this, but instead found that they contain observed spectra instead of properties like the mass, luminosity, SMBH mass, etc (take SDSS for example).
So, my question is, Is there any modern catalog of AGN and their properties?


texts: Are stars beyond the asteroid belt less constant?

texts:
If we graph the variability of a small bright star which is lined up with the asteroid belt, is it less constant than stars that are far away from the asteroid belt? To what degree does variability change relative to distance away from the most dense areas of the solar system?

I added the arrows to illustrate the question.


texts:
I understand this is an icky subject, but I recently got interested in units for large distances for applications in cosmology and what not (after hearing about the redefinition of the kilo and kelvin), and I was surprised to see many very weird units which seem difficult to use.

So I was thinking in astronomy distances only get larger and larger, so I looked to see if I could find any logarithmic scale for distances and I couldn't find any. Then again, I'm not an astronomer and not suited to argue anything.

Are there any logarithmic scales for larger distances, and if so why aren't they being used? And if non exist, is there a reason why(is it simply a bad idea)? Or is it simply a matter of keeping historical background?


texts: H-alpha velocity fields of spirals falling into a cluster

texts:
What kind of impact would you expect ram pressure stripping / tidal interactions / harassment / interactions with the cluster potential (etc!) to have on the h-alpha velocity fields of infalling spiral galaxies?
What I mean is, how easy is it to detect such processes at work, and how are you able to distinguish between these different mechanisms (using also h-alpha intensity maps, rotation curves, optical morphologies if available).

Cheers!


texts: Should the synodic period or the orbital period be used to determine the diameter of the Moon?

texts:
Aristarchus famously used a lunar eclipse to determine the diameter and the distance of the Moon, given that a lunar eclipse can last up to 3 hours and the angular diameter of the Moon is 0.5°.
Using this method, the diameter of the Moon is
$
\frac{(\textrm{earth diameter}) \times (\textrm{moon angular diameter})}{\frac{\textrm{duration eclipse}}{\textrm{orbital period of the Moon}} \times 360}.
$
Is it correct to use the orbital period here, rather than the synodic period? Should the orbital period or the synodic period of the Moon or some other period be used in this expression, and why?


texts: What is this thin, square-ish object on asteroid Bennu? How big is it?

texts:
What could this square thing be? Roughly how big is it? From BGR's Our first up-close look at the Bennu asteroid is a messy one:

rotated, 2x zoomed, and sharpened. unscientifically:


texts: What's the distribution curve for meteor sightings?

texts:
I know that meteor showers have a "peak" observation time.

What does the distribution in time look like? Is one side of the peak steeper/shallower or longer/shorter than the other side, and if so, why?


texts: Relative to the average age of other known planets, is the earth young, old or in the middle? Does it make a difference if you compare the earth against nearby planets (say < 500 LY), or other planets in our galaxy, or other galaxies?


texts:
In this image of LL Ori bow shock,

there is a smaller bow shock at the upper right.  Is that second bow shock substantially smaller than the LL Ori bow shock, or is it just much further away?  If the stars are reasonably close, is the upper star significantly smaller that it is producing a much smaller bow shock?  The LL Ori bow shock is measured about half a light-year across.  Any estimates of the size of the smaller one?


texts:
What is the biggest possible crater from an asteroid impact? Not asking for the biggest existing crater in the solar system. I should be able to find plenty of lists online. What I'm curious about is how big a crater can form before the impact results in both bodies reforming destroying near all evidence of the crater itself.

I don't mind erosion or normal geological processes  destroying the craters. That is just a matter of time.

Eg when the Mars size object hit the Earth. Both were substantially altered and incorporated in each other. Earth experienced a near complete reformation (in the spherical sense). Also resulted in the moon's formation. Obviously that sort of impact doesn't leave an 'obvious' crater.

I assume the makeup (mineral, size, speed, angle of impact etc) of both bodies will change the answer, so maybe a just a short list of sizes for the various xommon combinations?

Eg what would be the biggest crater possible on Earth before the Earth experienced severe...Um, reshaping?


texts: How do astronomers find the difference between a 'Cephid Variable Star' and distinct normal stars with opaque objects blocking it's light, like stars with planets revolving around them while both create a dip in the brightness-time graph at regular intervals of time, when this is how new stars are discovered?


texts: How do I align my finder scope National Geographic 76/700 EQ

texts:
Telescope :  National Geographic 76/700 EQ

I tried aiming my telescope at the moon but I just couldn't do it, it was so hard to do, my finder scope isn't helping at all and I watched a bunch of videos saying to use the screws to align the finder scope but the screws on my finder scope don't do anything. Any suggestions?? I really need help tonight is cloudy and I only get like 5 minutes every hour to look at the moon


texts: Are interstellar meteorites more common on the moon's polar regions?

texts:
Given that the rocks of the solar system mostly travel on the disc, is there any considerable probability that impacts on the moon coming straight up and down can be interstellar rocks?
If axis-aligned meteorites are very rare, then perhaps there is a chance that a significant number of axis-aligned impacts come from interstellar objects.
It would be fun to search the polar regions of the moon for meteorite impacts that were axis aligned in the hope that the impactor would be interstellar. How unreasonable is it? If I put a square of foam on the moon for 20 years, and I checked afterwards which objects had hit the foam at high speed from an axis aligned vector, perhaps I could find a rock from elsewhere in the galaxy?


texts: Why can't I use automatic photometry on IRIS?

texts:
I'm trying to do photometry on my stacked images of the night sky, but when I use the program IRIS and try to do automatic photometry, it always says it's a wrong image number and in every example of photometry the numbers have only 3 digits while my numbers are always 4 digits.

I've selected 3 objects that have the coordinates (360,3377) (591,2197) and (746,3437). The input generic name is the name of the folder with the pictures (FITS). I've also selected the aperture photometry option with the radius 8, 12 and 20. The coordinates VX and VY are both 0. The boxes "no matching" and "magnitude output" are selected. When I try to process it the program tells me "incorrect image number".


texts: Cannot calibrate “upgraded starpointer finderscope” for Celestron AstroMaster 114EQ

texts:
My wife just bought me an AstroMaster 114EQ which came with an "upgraded starpointer finderscope" -- it looks different than the one depicted in that link. I have tried following the instructions in their documentation to calibrate the finderscope with the primary telescope image and, unfortunately, the small red dot in the finderscope simply will not align with the main image of the telescope.

In attempting to calibrate it, I pointed the scope at a building about a mile and a half away and got it clearly focused in the main scope. I then looked through the starpointer finderscope and tried to adjust it but the range of adjustment would not allow me to line up the red dot with this building -- the dot was high and to the right and the adjustment knobs simply would not turn any more -- they were at the end of their adjustable range.

The supplementary documentation for the starpointer finderscope that came with the scope doesn't tell you which end points toward your target and which toward your face. I cannot really tell from the images in their website which orientation is correct. The mount doesn't seem to enforce any particular orientation. I assumed that the lense should be at the far end of the scope toward your objective and the power/brightness knob and the up/down adjustment knob, should be close to your face.

Can anyone suggest how I might remedy this? I did search here first and this other post did not seem to have the information I was after. I'm supposed to go camping the day after tomorrow and would love to be able to locate Jupiter. I'm concerned that the scope may have been incorrectly assembled...i.e., the mount is off or something.


texts: Does time flow in a Minkowski spacetime?

texts:
In a spacetime where the stress-energy tensor is null (no energy, no matter, no entropy), I wonder whether any motion of the variable time in the phase-space is well defined.
The arrow of time, meant as parametrisation of succession of changing events, might lose validity, since no events can occur without actors (particles or fields) that can generate them, right?
Could this be a paradox, when using the Minkowski approximation to propagate information?


texts: Any freely available large stellar spectra catalog?

texts:
For a non-astronomy personal project I would like to have a large set of optical stellar spectra combined with absolute magnitude when available. I search for a dataset that contains 10k - 10M objects, with total compressed size below 100Gb (ideally below 10Gb), is freely available via ftp/http/rsync and machine-readable. Presence of most 'naked eye visible' stars and their individual names in the set is desired, but not required.

I know that some digital survey data are freely available via FTP, so maybe some reasonable spectral data catalog exists as well?

Note, I'm planning to download the data for local processing, so retrieving them through on-line forms (or even automated http interfaces) is undesirable.

The best I was able to find is this catalog  . Dropping aside that FITS is not something I'm used to (this apparentrly can be rectified) it is too small. I'd like at least 1k stars, 10k preferable. There is apparently a lot of surveys in 0.1-10k objects range that are focused on specific type of stars (say, nearby M-class dwarfs) and stellar libraries containing spectral data on representative objects from various classes. However I'd like a 'representative set' here, which contains stars of various nature in proportion similar to their 'natural abundance' in some region. An example would be the set of stars of solar neighborhood above, but again it's too small.


texts:
What percentage of Earth-sized planets in a habitable zone can be detected by the radial velocity method?
I understand that larger planets and closer planets are detected more easily; and I assume that if a planet is in a circular orbit whose plane is nearly perpendicular to our line of sight, that the Doppler method won't be able to detect wobble of the star.
This question goes along with, but is of course different from, this question; but some of the factors like planet size and orbital radius enter in the same way, while the size of the star would enter in the opposite way.


texts: The moon: how to determine its size, speed and distance from earth using a simple telescope?

texts: Assuming I only have a simple telescope, how can I determine the size of the moon, its angular velocity and distance from earth?


texts: Derivation of the orbital parameters of a exoplanet discovered by direct imaging

texts: I wonder which orbital elements of a exoplanet can be found only applying direct imaging. I know that the angular separation combined with parallax can give us the semi-major axis, but what about the other elements? Is it possible? And what about the mass or the radius of the planet (given known mass and radius of the star)?


texts: Do the axes of rotation of most stars in the Milky Way align reasonably closely with the axis of galactic rotation?

texts:
The axis of rotation of the Solar System makes a large angle of about 60 degrees relative to the axis of rotation of the Milky Way.  That seems unusual - for example, most of the bodies within the  Solar Sytem are better behaved than that.
Do most stars or planetary systems in the Milky Way rotate in close accord with the galactic rotation?  Or is there a large scatter, so that, in fact, our Sun is not atypical?


texts: Why does radiation not need a medium to travel?

texts:
I wanted to know how radiation moves in vacuum of space and why it doesn't need any medium ?
( Like sunlight reaching a planet )


texts: Getting XYZ coordinates of Luminous Red Galaxies catalogue

texts:
So I want to get the XYZ (rectangular/Cartesian) coordinates of the LRG (luminous red galaxies) catalog. The catalog is available for download from here: https://data.sdss.org/sas/dr16/eboss/lss/catalogs/DR16/ You just have to search the "LRG" ones. Since I'm not very interested in clustering at first I figured I'd download the eBOSS_LRG_full_ALLdata-vDR16.fits. In this fits file, I see RA and DEC coordinates but I don't see any measure of distance. Thus I'm not sure how to covert this RA and DEC to XYZ coordinates. I've read some papers where they say they have done this so in principle it should be possible just I am not sure how. Am I supposed to use the magnitude to somehow estimate the distance (something like this: https://ned.ipac.caltech.edu/level5/Willick/Willick1_2.html)? For some reason, I expected this would be precomputed in the catalog measurements but maybe I'm misunderstanding something.
I understand that BAO (Baryon Acoustic Oscillation) is used for determining distance. According to https://www.sdss.org/dr16/spectro/lss/ the SDSS fits files link I posted above also contains information about BAO (it is the files that contain "rec" I am using the eBOSS_LRGpCMASS_clustering_data_rec-NGC-vDR16.fits file for example). However, I can't find what the fields mean and more importantly how to get distance from them.
Any and all help appreciated if I'm missing some documentation please let me know.


texts: How feasible is it that we could see the Central Black Hole Sgr A* occlude one of it's closely orbiting stars?

texts:
I'm thinking about the recent famous photo of a black hole, some months ago. It got me wondering if there isn't a way to more easily make a direct observation of these.

We detect exoplanets in part by phenomenae that occur when they transit their star.

We also have excellent time lapse photography of numerous stars orbiting the Milky Way's central Black Hole (Sgr A*), with timescales quite amenable to human timescales.

Could we observe Sgr A* directly by observing one of these stars passing behind, or almost behind it?

The diameter of the BH is estimated at 60m km, more than 40x the diameter of our sun (1.4m km). At that distance, parallax related effects and relative sizes wouldn't be an issue, as the star and BH are virtually at the same distance both very far from earth. A star also wouldn't have to be occluded, just pass close enough behind, for gravitational lensing to be detected on that fraction of its orbit (but not other places).

Additionally, a star could also be occluded by an accretion disk (if any), and its light affected in a way that would presumably show something of the nature of what it was passing behind. Admittedly Sgr A* may have little or no disk, but we might detect a disk of low enough density/size/activity not to be active, if a residual disk did in fact exist.

Are we likely to be able to see in time lapse photography, stars vanishing and reappearing behind an apparently empty patch of space, in this way? Has it been done?


texts: Rotation of the Earth about its own axis

texts:
I am wondering how the Earth got its original angular velocity. What was the cause that made the Earth rotate about its own axis?

What about its motion around the Sun? What gave the Earth the push to keep rotating around the Sun?


texts: I was reading about gigantic storms on giant gas planets, the great red spot on Jupiter and hexagon on Saturn to name a few, how about our Sun which is consist of plasma(hot gas which have some of their electrons stripped) why don't we see any big hurricane?


texts: Luminosity L(t) for a homologously contracting star

texts:
I'm dealing with a homologously contracting star with Mass M, Radius R and a gravitational binding energy of

$E = -a GM^2 / R $

(a is a constant).

I was looking for a way to find an expression for L(t), the luminosity as a function of time. Unfortunately, my attempts using time derivatives have not taken me far.

Thank you for your help!


texts: Will the detection of colliding neutron stars by LIGO help answer the question of where heavy elements came form?

texts:
I have read about and heard about the theory that most of the heavy elements we have here on Earth came from colliding neutron stars rather than by way of supernovae.

I'm not sure how strong this theory is, but I wonder if a LIGO (and backup observational/ gamma ray) detection would help answer this question in any way.


texts: Converting parsecs to light years in the dumbest way possible

texts:
I have to convert 132 parsecs to light years and I'm struggling to get the expected result. Here is my method:
$132 \text{ pc} = 132'' = 2,2' = 0,03(6)°$
I have an equation for stellar parallax which looks like this: $d = \Big( \dfrac{1 \text{ AU}}{\tan(0,03(6)°)}\Big)$
This should give me the distance to the object in Astronomical Units right? Well It doesn't and I have absolutely no idea why, I'd be very glad if someone could help me out


texts: Can the gravitational potential in a spiral galaxy be positive?

texts:
Thinking about this question I wanted to start with a rough model of the average gravitational potential of the Milky way. I ran across D. P. Cox and G. C. Gomez 2002 Analytical Expressions for Spiral Arm Gravitational Potential and Density which I think I can understand at least enough to script it. They started with an analytical density distribution and approximated its potential with an analytical form, later they solved for the exact density which generates it, but I am not using that.

I calculated the first example discussed in Section 4 and at least at first glance it seems to agree with their figures. At large distances the potential tends to zero which is good, but the modulation is both positive and negative! This is true both from my script and in their figures.

Without a repulsive force, I don't think the potential can be positive. What am I missing?

Note 1: I've plotted for $z=0$

Note 2: I'm using kg meters and seconds for units, so the plotted potential is in m^2/s^2.

import numpy as np
import matplotlib.pyplot as plt

def PHI(r, phi, z):
    term_1 = -4 * pi * G * H * rho_0
    term_2 = np.exp(-(r-r_0)/Rs)
    gamma  = N * (phi - phi_0 - np.log(r/r_0)/np.tan(alpha))
    K      = n * N / (r * np.sin(alpha))
    KH     = K * H
    beta   = KH * (1 + 0.4*KH)
    D      = (1 + KH + 0.3*KH**2) / (1 + 0.3*KH)
    term_3 = ((C/(K*D)) * np.cos(n*gamma)) * (np.cosh(K*z/beta))**-beta # sech is just 1/cosh

    return term_1 * term_2 * (term_3.sum(axis=0)) # sum over n

G      = 6.67430E-11 # m^3 / kg s^2
parsec = 3.0857E+16 # meters
mH     = 1.007825 * 1.660539E-27 # kg
pi     = np.pi

N     = 2                        # number of arms
alpha = 15 * pi/180.          # pitch angle
Rs    = 7000 * parsec            # radial dropoff
rho_0 = 1E+06 * (14./11) * mH    # midplane arm density
r_0   = 8000 * parsec            # at fiducial radius
H     = 180 * parsec             # scale height of perturbation

C = np.array([8/(3*pi), 0.5, 8/(15*pi)])[:, None, None]
n = np.array([1, 2, 3])[:, None, None]

# plot it
hw = 30000 * parsec
x = np.linspace(-hw, hw, 200)
X, Y = np.meshgrid(x, x)
r = np.sqrt(X**2 + Y**2)
phi = np.arctan2(Y, X)
z = 0.

phi_0 = 0.

potential = PHI(r, phi, z)

if True:
    plt.figure()
    plt.imshow(potential)
    plt.colorbar()
    plt.gca().axes.xaxis.set_ticklabels([])
    plt.gca().axes.yaxis.set_ticklabels([])
    plt.title('+/- 30 kpc')
    plt.show()


texts: Does parallax measurement depend on position in the sky

texts:
Naturally, the parallax is easier to measure for stars that are closer than farther away. But if all stars were the same distance from the Sun, and if there were some other reference to measure the parallax, would all stars show the same parallax?
In other words, does the position of a star (the right ascension and declination) affect the parallax measurement and calculation? For example, are stars near the ecliptic or equator or celestial pole easier to measure than other locations on the sky?
Feel free to include any equations or references if it helps.


texts: How could a supernova seed solar nebula?

texts: If the heavier elements such as Uranium came from a supernova, then this supernova had to sit somewhere right in the middle of the original solar nebula, because although the ejected matter traveled extremely fast by star or planet standard, it was still not fast enough to truly get across the empty space between clusters of stars. Does this mean the supernova was actually birthed and died in the same nebula or at least in the immediate vicinity in a region that is rich in hydrogen? Could the solar system be still in this nebula? What could endow the solar system as a whole with so much momentum that it acquired a different trajectory around the galaxy than its mother nebula, if the solar nebula is in effect no where to be found?


texts: What kind of telescope should I get my husband?

texts:
I'm very much an amateur when it comes to telescopes. My husband wants one for his birthday. I'm willing to spend up to $900 on one. Can any of you gurus give me advise as to which one I should buy?

Thank you so much in advance!


texts: Wavelengths for observed objects -- emitted or observed?

texts:
The WISE craft (Widefield Infrared Survey Explorer) surveys the sky in 4 wavelength bands; 3.4, 4.6, 12, and 22 $\mu$m. When it's observing an object with an estimated redshift (given by

$z = \frac{\lambda_{obs} - \lambda_{emit}}{\lambda_{emit}}$

from Wikipedia) of, say, 0.373 (the lowest redshift for one of the objects I'm studying), would the wavelength it's seen in be its observed wavelength? I'm interested in calculating the wavelength actually emitted by the object.


texts: How to determine zenith coincidence from date time data sets

texts: I have two or more sets of  dates and times for which I am interested in the location of the Zenith at my location and whether they are coinciding. So far I have been comparing pairs of them on two Stellarium windows with the azimuthal grid but its laborious. Can any one tell me of an easier way. I expect I could do it in excel with a bit more knowledge.


texts: I have read that the Big Bang created space-time, but how could this be possible? The Big Bang was itself a singularity, and a singularity is a point in space-time where the curvature becomes infinite. So how could the Big Bang create something without which its existence would not have been possible?


texts: What visual artifacts are expected from the JWST?

texts: What visual artifacts should we expect from the images that will be released from the James Webb Space Telescope? Specifically, do we expect 3-pronged diffraction spikes (any preview how they would look?) and do we expect any artifacts due to the honeycomb-like structure of the main mirror?


texts: What causes celestial bodies to move like they do from Earth's surface?

texts:
As you probably know, the planets have pretty predictable orbits around the sun but what exactly causes the complex movement of celestial bodies in the sky from Earth's surface? Mars is an excellent example of this.

Mars example


texts: How bright is Andromeda's center, in magnitudes per square arcminute or something similar?

texts:
I'd like to know how bright the Andromeda galaxy's core is as an extended object, not the total integrated brightness.

Ideally a contour map or scan across the center might show brightness in magnitudes per square arcminute or square arcsecond. Or a low power digital photo with some kind of brightness scale per pixel. Older images such as the one below are from emulsion and so if they are just scanned and uploaded they will not be linear.

I don't even know where to begin to look for such a thing. Thanks!

Below: "This picture shows M31 (NGC 224) and its small companions M32 (NGC 221), lower center, and NGC 205 (sometimes designated M110), to the upper right. The image was made by combining three separate frames derived from photographic plates taken in 1979 at the Burrell Schmidt telescope of the Warner and Swasey Observatory of Case Western Reserve University (CWRU)." From here.


texts: The star is located at a distance of 163,000 light years in the constellation of Circinus.  As the Milky Way is 100,000 light years, this would then imply the star is outside the Milky Way?  Would it be a data anomoly if that is the case or is it in another galaxy like r136a?  Would it be on the far side of the galaxy, other side of the Galactic Centre?


texts:
I recently read some articles and pages on Solar Sails, and the possibility of using lasers to propel spacecraft, and I had a relatively outlandish idea.

Would it be possible for a star to be outputting enough light that planet-sized (or smaller) objects caught in it's gravitational pull would not cross a certain threshold?

A sort of 'reverse blackhole' if you will, where the event horizon is an area that the matter(not light) can not proceed further into the star.

I would assume this to look like a star with a large ring around it, equidistant from any point of the star's center, where matter would coalesce.

Furthermore, would it be possible that an object could remain 'stationary' (ie. not in orbit and no acceleration in any direction beyond the pull of gravity) around this star without fear of gravity pulling it into the star?


texts: When we see the Sun, do we actually see its past?

texts:
The Sun's rays hit our eyes around 8 minutes after they are emitted from the Sun.
Does this mean that the Sun that we see is always the Sun as it was some 8 minutes before? I strongly think this must be happening; is it really a fact? Do we always see the Sun's past?


texts: How much does a linear lightyear of space expand in a year?

texts: Now that we know that the universe is expanding, how much does a linear lightyear of space expand currently in a year?


texts: What would stargazing be like at the edge of our galaxy?

texts: Let's say, for the sake of speculation, we acquire the technology necessary to travel to the outer edge of one of the spiral arms of our galaxy. We go to a star in this "outer rim" and land on a planet orbiting a star there. What would we see when our side of the planet is facing outward from the galaxy? (Assume no atmospheric interference.) The answer will, of course, depend on the galactic coordinates of the star we choose to visit. Provided a particular set of coordinates, how much do we know about what we could see with the naked eye or through some form of optical instrument? I'm more interested in our ability to answer the question, rather than the specific objects we'd see (although they're pretty interesting too). You're welcome to select an arbitrary but still useful and appropriate boundary as the edge of the spiral arm.


texts: How would Jupiter's brightness relative to our sun seem to a remote observer (observing from a remote star)

texts:
Given that Jupiter is 5 AU from our sun and a remote observer viewing our solar system from some other part of our galaxy looks at it. We assume that Jupiter's radius is $11 \times 6700$ km.

What would be the relative brightness (luminosity?) of Jupiter relative to our sun's?


texts: How do we know Nemesis is not a black hole (or neutron star)?

texts:
Nemesis, the hypothetical "death star", is supposed to be a massive body that orbits the Sun at long distances and periodically sends comets from the Oort Cloud into the inner solar system. These comets impact the Earth and cause extinction events. It hasn't been found, and the theoretical case for it is not compelling anyway.

My question here is about this curious line from Richard Muller's page at LBL.

  Fortunately, several all-sky surveys are underway that should find Nemesis in the next few years, if it is there, and rule out Nemesis if they don't. (Nemesis could hide if it were a black hole, but that is not very plausible.) These surveys include Pan-Starrs and the LSST.

How do we know it's not plausible for Nemesis to be a black hole? For that matter, how do we know it's not a neutron star?


texts:
My question is seen in the title: What is the right ascension overhead at Greenwich at noon on 21 march

I'm a little bit confused since the right ascension is set by the vernal equinox and don't understand how this is related to Greenwich.


texts: Is there any way to seperate astronomical and instrumental objects?

texts: Here is a image of hcg79 taken from APO. I'm just curious if there is any way to seperate astronomical and instrumental features in this picture? Thank you.


texts: Are ocean water planets at Mars' atmospheric pressure possible?

texts: Can water planets exist whose atmospheric pressure at sea level is just above the triple point of water, say at about 690 Pa (0.1 psi)? If no, why not? Just curious. How thick or thin can atmospheres of ocean planets be?


texts:
The Hour Angle (HA) is measured west from the observer's meridian in hours, mins, seconds.

How is the Hour Angle used to help plan observations during the night at a telescope?


texts: If the moon's orbit decays- how would it effect the moon's phases?

texts: If a planet passed near the moon and caused its orbit to decay down to earth- how long could it take and how would that effect the visible phases of the moon on earth?


texts: When is the best time to observe M81 from the Northern Hemisphere?

texts:
I have read that the best time to view M81 is during the spring. Considering its RA is ~10h and Dec. is +69°, wouldn't February 21st be the best time to view it since this is about when it transits my meridian at midnight or are there other considerations?

I'm observing from Cleveland OH, USA area; 41.5° N, 81.7° W.


texts: Where can I find a catalog of all stars in the Milky Way?

texts: Is there a catalog of all known stars or brightest stars in our galaxy? Preferably with some sort of galactic coordinates instead of just night sky coordinates (right ascension, etc.) I'm trying to make a model of the milky way, explorable with an oculus rift.


texts: Any information on the salt content of Mars' atmospheric dust?

texts:
Answers to and comments on How to drink water on Mars? suggest that one would not want to drink melted water ice obtained from exposed surface deposits near the poles because it may contain various salts and other dangerous chemicals (perchlorate salts are one particularly nasty suspected component of mars soil and it's water content).

Mars' atmosphere contains dust even when there are no dust storms, and in this answer it is explained to be the cause of the reddish color of the Martian sky as has been photographed by several Mars landers and rovers.

Are there any measurements or even models or predictions on how much of the particulate matter in Mars' atmosphere could be tiny particles of salt, or salt mixed with other minerals? Put more simply, how salty might Mars' atmosphere be?

Martian sunset (credit: NASA/JPL-Caltech/Texas A&M/Cornell) borrowed from this answer.


texts: Why did the edge of Olympus Mons collapse?

texts:
On Earth, the maximum height for a mountain is ~10 km. Beyond that, the mountain will start to spread or collapse. On the surface of Mars, the gravity is not as strong, so the maximum height for a mountain is higher.
The edges of Olympus Mons are very steep cliffs, rather than being a shallow slope all the way down. Surrounding the mountain, there is a large aureole that looks like it might be left over from landslides.
Did the edges of Olympus Mons collapse and cause a landslide because the mountain reached the maximum height for Mars? Or was some other process involved?


texts:
I know that there has been conflicts between scientists and the native population. Astronomers want to build new telescopes on Mauna Kea, however, several sacred sites would have to be built on.

My question is, are there any current plans to move forward with the observatories, or have they reached a gridlock?


texts: How many arms does the Milky Way galaxy have?

texts: How many arms does the Milky Way galaxy have and how is it determined?


texts: Computation of mean sidereal time at Greenwich using solar position algorithm

texts:
Using Equation 28 in Section 3.8.1 of Solar Position Algorithm (Reda, I. and A. Andreas, Jan. 2008), I computed the mean sidereal time at Greenwich for 2003 October 17 for four different times (UT), using a Casio fx-991MS. The computed values were cross-schecked online using the URL Computation of GAST, GMST, and ERA

Equation 28 used to compute GMST is:

v0=280.46061837 + 360.98564736629*(JD - 2451545) + 0.000387933*JC^2 - JC^3/38710000

JC is computed as:

JC = (JD - 2451545)/36525

The computed values of JD and JC are as follows:

1. 00:00:00 UT: 2452929.5   (JD) & 0.037905544 (JC)
2. 05:30:00 UT: 2452929.729 (JD) & 0.037911818 (JC)
3. 11:00:00 UT: 2452929.958 (JD) & 0.037918083 (JC)
4. 19:21:00 UT: 2452930.306 (JD) & 0.037927611 (JC)

However, there is a clear offset between the computed values and the values provided by the aforementioned URL. For example:

1. 00:00:00 UT: 22.32738 hour    (Computed) & 1.6726265 hour (URL)
2. 05:30:00 UT: 16.7231 hour     (Computed) & 7.1960077 hour (URL)
3. 11:00:00 UT: 11.30528667 hour (Computed) & 12.702743 hour (URL)
4. 19:21:00 UT: 2.93042 hour     (Computed) & 21.075605 hour (URL)

Moreover, if I subtract 22.32738 hour from 24.0, I will get 1.67262, which is the value provided by the URL.

At the same time, using the same set of equation , if I compute GMST for 1987 April 10 at 00:00:00, the computed and URL values are the same.

April 10 at 00:00:00:

JD=2446895.5
JC=-0.127296372
GMST = 13.18 hour (Computed) & 13.17954 hour (URL)

Kindly help me to understand where exactly lies the problem. If the problem lies with the concept regarding the interpretation, please help for a better understanding.

Note: Knew gmst is now deprecated , but since i am a beginner thought of understanding gmst foremost and then will dwell into current scenario.

Thanks.


texts: What does the Sun look like from the heliopause?

texts:
I calculated the angular diameter of the Sun at the heliopause to be 0.004°.  If that is correct, would the Sun appear as a disk, or like the pinpoint of light from a star?

How bright would the light from the Sun appear?  I understand at Pluto the Sun appears as bright as the full moon at night on Earth.  Assuming the heliopause is 3x distant from the Sun as Pluto, does that mean there would be 1/9th as bright at the heliopause.  What would that brightness translate to an everyday measure?


texts: Could an orphan/rogue planet have a moon?

texts: Is there some reason why an orphan or rogue planet wouldn't have a moon? Let's say it started out in a normal system and then just got flung out by an unstable orbit.


texts:
As Venus rotates in clockwise direction, while other planets rotate in anti clockwise direction:

Is it possible that Venus was once a rogue planet?


texts: Does General Relativity really predict Black Holes?

texts: I'm doing some research on black holes for a science video contest. I want to explain the physics of how they work, but also want to have a little background on how they're formed. As far as I've searched, black holes are predicted by general relativity (GR). But I saw this site that said 'general relativity is inaccurate at very small sizes' and that it kind deviates from GR. So I want to confirm whether black holes really are a prediction of GR or an inconsistency with GR. Can someone please help? Thanks.


texts: If a star were to suddenly lose nearly all of its stored heat, would it be able to return to its normal state?

texts: If not, would it be possible to approximate the maximum heat energy a star could lose before the change became irreversible?


texts: What is the current angle of motion of the sun with respect to the Galactic Plane?

texts:
I understand that the solar system oscillates in its motion around the Milky Way. However at any given time, there must be a specific angle between the current direction of the solar apex and the galactic plane. This is the angle - in degrees - I am looking for.

To be specific. I'm not looking for the angle of the solar system with respect to the galactic plane, nor the angle between the celestial pole and the galactic plane, nor the angle between the plane of the ecliptic and the galactic plane. I am only looking for the current angle of motion between the solar apex and the galactic plane.

Also, is there more clear terminology for this? I've spent a few hours searching and it seems that I can't find an answer to what I would imagine is a relatively obvious question. Am I searching with the wrong terminology?

Thanks.


texts: Can the WISE telescope detect black holes?

texts: Black holes are hot, aren't they? With its infrared scan, could the WISE telescope also detect a black hole? The hypothetical planet beyond the Kuiper belt could actually be a primordial black hole. The WISE telescope might already have imaged the object but could it have done it also if it is a black hole?


texts: Estimating close approach between all asteroids themselves

texts:
I am currently writing a C++ program to show asteroids in 3D, and find close approaches or collisions. I got my orbital elements from JPL https://ssd.jpl.nasa.gov/sbdb_query.cgi. So far so good, with over a million asteroids drawn in 5ms with my old Quadro GPU
But the problem is the variation of the elements over time. For example, CERES:
epoch,a,e,i,om,w,ma
2459200.5,2.766089105818,.07816842657453,10.58789954719,80.27235841368,73.72488984426,205.5454154582
2459310.5,2.765760313090,.07831877879848,10.58807660401,80.26860808947,73.73699886586,229.1146825391

After only 4 months, the eccentricity and all other elements have changed as seen on the second line.
How can I compute the change in the parameters without knowing their derivatives?
Or where to get those derivatives?
I searched all JPL small bodies site and their telnet access or email, but could not find a way to download orbital elements with derivatives or a way to compute the change.
I am aware that the difference might be just a pixel on the screen but it represents hundreds of thousands of kilometres. What I want to do is study the close approach between the asteroids themselves and eventually near collision. I already did that for artificial satellites using SGP4 propagator using OpenCL running on GPU video card. I can propagate 20,000 satellites (include debris) in a few milliseconds and get results exact to 1 kilometre. Compare with Celestrak Socrate. A prediction of a 1,000-kilometre approach must be possible.
Does anybody know how?


texts: Why are quasars so far away that they couldn't be optically resolved in the 1950's?

texts:
Wikipedia's Quasar includes the following in its introduction:

The term quasar originated as a contraction of quasi-stellar (star-like) radio source, because quasars were first identified during the 1950s as sources of radio-wave emission of unknown physical origin, and when identified in photographic images at visible wavelengths they resembled faint star-like points of light. High-resolution images of quasars, particularly from the Hubble Space Telescope, have demonstrated that quasars occur in the centers of galaxies, and that some host-galaxies are strongly interacting or merging galaxies.

So today instead of "quasi-stellar" we might simply say "unresolved". The light is star-like because the light from galaxies has a strong stellar component. (this second sentence is argued against in comments)
Why are quasars so far away that they required high resolution techniques (i.e. space telescopes or adaptive optics) to resolve them? Is it just that they are fairly rare and a roll of the dice resulted in none close enough to be resolved in older large telescopes of the 1950's, or are there some cosmological effects in play as well?


texts: Does the major axis of the moon's orbit point in the same direction (with small deviations) throughout the year? or does it migrate along a path so that after a million years it might be 90° away from where it started?


texts: How close would the orbit of Mars have to be to that of the Earth to induce a collision?

texts:
When the Earth passes by Mars they exert a slight gravitational pull on each other, but the force is so small that their orbits are not significantly disturbed.

However, if we imagined that the orbits of the Earth and Mars were coplanar and much closer to one another, then there would presumably be some critical distance at which they would move together and collide.

What is that critical distance? In other words, if we shrunk the radius of the orbit of Mars, how much would it have to shrink before a collision would occur by the natural force of gravity between the two bodies?


texts: What is the probability that there is life on other planets?

texts:
From a mathematical point of view,  what is the probability that

1) There is organic life on other planets

2) There are advanced species like us or even greater than us on other planets?

Is there a formula or equation or a way we can calculate this probability?


texts: Determining moonset time from Nautical Almanac

texts: I have recently learnt to determine moonrise and moonset times using the Nautical Almanac, as part of my maritime navigation course. I have a query regarding the determination of moonset times. I will use an arbitrary date and an arbitrary latitude to illustrate my confusion. On 3rd February 2020, at the equator, the Nautical Almanac tells me that the moon will set at 0041 hrs. Does this mean that the moon that rises on 3rd February 2020 sets at 0041 hrs on 4th February 2020 or does this mean that the moon that rose on 2nd February sets at 0041 hrs on 3rd February 2020?


texts: The size of the radius of the event horizon of a black hole created by the merger of a black hole binary system

texts:
Let's assume that you had a black hole binary system and everything said here is possible. Their large masses would lead to a large emission of gravitational waves. The loss of orbital energy and angular momentum to this gravitational radiation should ultimately cause the two black holes to merge into a single black hole containing the combined mass of the merged black holes.

With this said, does a greater combined mass of the newly formed black hole mean that the radius of the new event horizon is greater than the radius of the event horizons of the singular black holes?
I don't know if there is a formula connecting mass to radius, or if this is essentially a conceptually hypothetical concept, and the answer is simply that the larger the mass of the black hole, the larger the radius of its event horizon


texts: Why not send a Gaia-like mission to Mars?

texts:
This answer to the question why we didn't send Gaia to Neptune's orbit raises the question of why we don't send a Gaia-like mission to the orbit of Mars. It seems like it doesn't have the problems mentioned in the answers, and it would make it possible to measure parallax for stars 50% further.

orbital speed: waiting 6 extra months to get better precision seems like a better trade off than waiting 9 years to get the same precision as Gaia;
partial coverage: after two years, the entire sky could be covered. Far from the 168 years for Neptune;
telemetry: sending back data from a Gaia-like mission can't be that much harder than sending back data from any other of the tens of missions to Mars;
power: the solar panels don't need to be 900 times bigger;
radiative environment: contrary to Jupiter, Mars doesn't have a magnetosphere, so the spacecraft wouldn't be disturbed by it.


texts: Theoretically what happens to a black hole that evaporates?

texts: Theoretically, does an evaporating black hole remain a black hole until it evaporates to nothing? Or does it change into something else once it evaporates to below a certain mass?


texts: Can we know where (South, East, West...) the moon will be at a specific time?

texts:
Apparently, a few nights from now (more specifically on the night between the 27th and 28th of September this year, nights being Belgian nights), we will have a lunar eclipse.

That's great, and I wish I could find a nice spot to go see that with friends!

Sadly I never took a lot of time watching the moon with a compass in my hands, so I'm wondering:

Can we know at what orientation (as in North, South etc) will the moon show up from Brussels between 12PM and 4AM GMT in the night of 27th to 28th September?

What are the calculations and/or data source involved?


texts: How to calculate the distance to galaxies with standard candles?

texts: I was wondering how the distance in Mpc could be calculated between Earth and a galaxy using the luminosity provided? Do not be shy to use all math necessary :)


texts: Are there gas clouds in space so dense that we couldn't see out of them if one where to be inside it?

texts:
The images of telescopes capturing gas clouds are quite intriguing to me, which keeps me wondering about visibility inside them.
Are there gas clouds in space so dense that we couldn't see out of them if one were to be inside it?
Or are even the densest ones still sufficiently transparent that we could see stars and constellations from the inside?
I'm not asking about dust clouds which can certainly be quite opaque in visible light.


texts:
I have an assignment, where I'm supposed to estimate the temperature of a star in at least two different ways, and determine which of the approaches gives the most reliable estimate. All that is given is the star's brightness at some random wavelengths. One way of estimating would be finding the peak brightness from the data, and use the corresponding wavelength as peak wavelength and solving

$$T = \frac{b}{\lambda_{max}}$$

So I've got 20 different wavelengths, ranging from 90nm to 1000nm. How would one go one about estimating T from a blackbody spectrum? Should I graph one with the given wavelengths and try different values for T until it fits the data?

However, I can't think of any other approaches with so little data.


texts: Why not us interferometry to take a picture of Pluto?

texts:
Interferometry is among the best ways (if not, the best way!) to have an image of a very distant object.

Recently a picture of the black hole at the center of M87 was released. It is the result of several data collected by the Event Horizon Telescope, a series of arrays all across our world, working as one like a giant Earth sized telescope. The picture is not really cutting edge and high definition however it is still very surprising and in a way detailed enough, considering the fact that M87 is 53.49 million light years away... and this is where I arrive to Pluto which is just around 6 to 7 billion kilometers from us.

If we used an interferometer, perhaps the same size as the EHT (or just a smaller one, the size of an entire continent), and point all the arrays at Pluto, then we should have a picture with a resolution that is at least higher as the Hubble Space Telescope, but likely not as high as the pictures from the New Horizons spacecraft which directly made a fly by of Pluto... right?

If so then why don't we use interferometry to take pictures of Pluto from Earth?


texts: Is there a formula for absolute magnitude that does not contain an apparent magnitude term?

texts: I have a star that I need to calculate the absolute magnitude of. I am given the temperature, luminosity, radius, mass, and distance in light-years. So I am wondering, what is the formula to compute this, using only these terms?


texts: What's the difference between a crater and a basin?

texts: When I was searching the name of the Moon's largest crater, many websites said that it was the South Pole-Aitken Basin. But in some definitions I've found, the word "crater" is used to describe smaller impacts on the Moon surface, and since the South Pole-Aitken Basin has a diameter of almost 2500 km, I'm not sure if you could say that the South Pole-Aitken Basin is the Moon's largest crater.


texts: What does correcting for LSR mean in galactic velocities?

texts:
This is a two-part question, but both parts are related:

I'm aware that modern astronomical software can correct velocities for the local standard of rest (LSR), but what does that really mean? As in, if you have measured a radial velocity by hand (e.g., from a plot of a spectral line) and you want to correct for LSR, how is this done?

As an exercise, I want to compare the galactic proper motions (which I presume are another way of saying velocities?) of a group of stars within 2kpc from the Sun between a method described in Eqs.30-32 of Mignard 2000 (Hipparcos data), and Eqs. 1-2 of Bovy 2017 (Gaia data). Apparently I also have to correct these velocities for LSR, but how is that done? Do you add a specific value? I thought these equations already include the components of the Solar motion w.r.t. to LSR, unless the constants included in the equations have nothing to do with that. I'm probably missing a big point here and books haven't helped me at all.

Thank you in advance.


texts: At what latitude could Orion's belt and Aldebaran be ~10 degrees above the horizon at the same time?

texts:
In his appearance on television contained in the video The Mystery That Keeps Neil deGrasse Tyson Up At Night, in the backdrop behind astronomer and educator Neil deGrasse Tyson and the talk-show host, what latitude on Earth would have Orion's belt and Aldebaran at equal elevation (about 10 degrees) above the horizon? Could that be Sunrise/Sunset, or are those just city lights?

He's known to be a stickler about such things (the story about the stars in the movie Titanic for example). This background must be calculated from a particular latitude at least (if not longitude and/or season).


texts: How to properly observe Solar Total Eclipse in 2019?

texts:
I live in South America and I'm willing to travel to Chile in July 2019 to observe (in a curious way, not professional) the Solar Total Eclipse.

According to my research, one of the best cities to observe the eclipse is in the coastal city of La Serena at 3:20 PM Local Time. However, I don't know if it can be seen from "anywhere". I was thinking of observing it from the beach. Does that make sense?

I also know that I need some kind of special sunglasses for safety. I found some on Ebay but I don't know if they are authentic. I would appreciate if someone could point me to a website that sells authentic eclipse glasses for a reasonable price and international shipping.

In short, my question is, will I be able to amazingly see the eclipse by just traveling to La Serena and go to the beach on the specific day and time? Is there a better place to see it? Is it better to see it from a high ground? Any tips are welcome.

Thanks.


texts: Can a frost line exist around a protoplanet?

texts:
The Frost line is the border that marks where volatiles such as water, methane, ammonia, etc. (commonly referred to as 'ices') are able to condense into solid grains in the protoplanetary disk around a forming protostar. Beyond this border, these ices form a significant part of any coalesced planetary body (like the many icy moons of the gas giants), whereas inside this border, the bodies that form are primarily rocky (the four terrestrial planets, Mercury, Venus, Earth, Mars).

Can such a frost line exist in the accretion disk around a hot gas giant such as a proto-Jupiter?

Some soft evidence for this: Jupiter's four Gallilean moons are of similar sizes and follow a clear trend from the innermost outwards:

Io: Mostly silicate rock and iron sulfide. Density is 3.5 $g/cm^3$.
Europa: Mostly silicate rock with an estimated ~100 km layer of ice/water. 3 $g/cm^3$.
Ganymede: Silicate with an estimated ~800 km layer of ice/water. 1.9 $g/cm^3$.
Callisto: Approximately 50% ice. 1.83 $g/cm^3$.

Source: Mainly articles in Wikipedia

Now, there are other mechanisms by which ices can be disproportionately lost from Io, mainly through its extreme volcanism. But this doesn't necessarily explain the trend seen in the other moons.

To be specific, I'm not asking if a protoplanetary frost line is responsible for the distribution of elements in Jupiter's moons, merely if such a frost line can exist and contribute to the observed element distribution.


texts: SDSS ImgCutout webservice returns black image for dr12

texts:
The SDSS (Sloan Digital Sky Survey) ImgCutout webservice should return jpeg images for a given field that is defined by the parameters. The service can be tested here: http://skyservice.pha.jhu.edu/DR12/ImgCutout/ImgCutout.asmx?op=GetJpeg

A simple (and working) get query is given here:
http://skyservice.pha.jhu.edu/DR12/ImgCutout/getjpeg.aspx?ra=132.749&dec=11.656&scale=0.79224%20%20%20&width=400&height=400&opt=

If you enter the same information (the parameters) in the form of the first link and click on invoke you will get a black image only. You can test the base64 encoded result here: http://www.askapache.com/online-tools/base64-image-converter/

Description of how to reproduce my findings:

Go to http://skyservice.pha.jhu.edu/DR12/ImgCutout/ImgCutout.asmx?op=GetJpeg
Fill parameter 'ra_' with '132.749'
Fill parameter 'dec_' with '11.656'
Fill parameter 'scale_' with '0.79224'
Fill parameter 'width_' with '400'
Fill parameter 'height_' with '400'
Press 'Invoke' button
Convert the content in the <base64Binary> tag from base64 to a jpeg

Following this steps I always get a black image.

Now the question:

Do I require an additional parameter (non empty string) for either imgtype_ or imageField_ in order to not get the correct image? What are this parameters good for anyway?

(Is there a better place this question? It would be nice if there was a tag for SDSS)


texts: Why in my area does NEOWISE appear so dim and small?

texts:
So, I was always amazed by images of NEOWISE around the Internet like this:

Or this:

Yet, all my efforts to see it or photograph it in its full glory were fruitless...

22.07.2020 22:01
Here you can barely see it at the bottom-left of the image...

24.07.2020 22:00
Here is the zoomed version... Very very blurry. The point is that I couldn't even see it with my "naked eye" (well I couldn't see it even if it were much brighter, because I use glasses, and that's automatically not "naked eye", but yea). The maximum that I could see was just some smudge. With 5x binoculars I could see it, again super dim and blurry. I decided to purchase a telescope specially for this, and although I could see Jupiter's moons and Saturn's ring quite clearly, I had no success with NEOWISE. Both at 56x and 140x zoom the comet seemed super blurry and dim. Although stars around it were in good focus, no matter how I tried to focus the comet itself, it always seemed out of focus...
BTW, these 2 shots were taken at the closest approach to Earth around 2
So I thought, maybe it's because of light pollution? I live in a not-super-giant city, but a light pollution map showed some amount of pollution still. So I went to a light grey area (only one step brighter than black) on the map. This, however didn't change much at all...

25.07.2020 22:32
The comet is still very dim and small. I couldn't find it with the "naked eye" reliably. Its size is almost the same as surrounding stars, yet on other people's photos it appears like 10 times bigger than the stars around it!
What could be the reason for this? If not light pollution, maybe it's that my location is very bad for viewing it? I'm located in southern Ukraine, Kherson city.


texts: Calculating the Solar Day of an Exoplanet?

texts:
I am currently in the process of compiling a list of stars and their planets, given the information in the European Star Catalogue found here, but I'm struggling to find out how to calculate a planets solar day. To be exact; How long, in earth hours, is the solar day of a planet found in this catalogue?
I know the catalogue is incomplete and that it's likely impossible to calculate the solar day for some of these planets due to this, but that's okay. I could also accept the sidereal day rather than the solar day.
I tried to use the formulas found here but I have a hard time finding out what numbers to plot into the equations, given the information available in the exoplanet catalogue. I've been doing a lot of googling and I'm not an astronomer, so it has been a bit of challenge!
I hope some of you can help me here.


texts: Type Ia supernova are used as standard candles. But they also are transient events. This means that to determine the distance of a galaxy using supernovae, you have to wait for one to occur. How often do type Ia supernovae typically occur in a galaxy ?


texts: Can we discern black holes with visible light?

texts:
Sorry for my dumb terms. I'm interrested in astronomy but I have next to zero background.

Given that a black hole absorbs everything, including light, could we ever discern one with visible light (and live to pass the information on)?

This question contains one generated picture of a black hole and Google image shows visual representations that all look similar (black circle in the centre, light that's distorted around it and the further we go away from the center the background is less and less distorted), but are those actually representative? Is there really a black spot in our vision field at the place where the black hole is? Both the answer to the question and this page discards such images as "fantasy", but they don't really answer the questions I'm asking, which are:

Will we ever be able to discern a black hole with visible light and live?
If we can, what is a currently acceptable description of what we'll see with visible light? I don't especially expect a picture, so a textual description is also good, but keep in mind it's in regards to visible light. Other questions on Astronomy SE explain what we can "detect" using radio waves or other means of observation.
In 2014-2015 CERN said they might be creating micropscopic short-lived (10-27 seconds) black holes with the LHC (and this lead to a global nonsensical fear that it'd destroy the planet). Did they create any? If yes, was there any opportunity to picture them despite their tiny size and short life?


texts: What actually determines the angular uncertainty of the source of a detected gravitational wave?

texts:
This answer and comments got me thinking. Astrometry 101 tells us that while we can use $\lambda/D$ as an estimator of resolution, if we can assume a point source we can determine the centroid or position to far higher precision.

For example, GAIA's design targets for precision were roughly 7, 20, and 200 micro-arcseconds for visual magnitudes 10, 15, and 20, respectively whereas $\lambda/D$  gives 70,000 x 200,000 micro-arcseconds for its rectangular mirror.

The limitations are both instrumental beyond just the aperture or baseline, and connected to the nature of the signal, and that's were determining the direction of a gravitational wave source is very different than determining the direction of a star's light.

Question: For gravitational waves then, what actually determines the angular uncertainty of the source direction? Does it turn out to be baseline-limited (e.g. $\lambda/D$) or instrument-limited, or limited by the very short-lived and chirped nature of the signal? Or is it something else, perhaps in the modeling and reconstruction of the event itself?

From ligo.caltech.edu's Gravitational-Wave Observatories Across the Globe just for background:


texts: Moon, center of mass & geometric center, tidal locking

texts: Since the moon is tidally locked to earth, what about center of mass and geometric center? How far from each other are they? Can a celestial body be tidally locked to an other one if its mass distribution is perfectly homogeneous (center of mass at the very same place of geometric center)


texts:
Given our knowledge and the standard cosmological model, we estimate that the age of the universe is about 13.7 billion years old.

How much sense does it make to talk about the age of the universe as a whole?

We can observe time dilation so we know time passes differently for observers moving at different speeds (special relativistic time dilation) or located at different distances from centres of strong gravitational fields (as explained by general relativity). Is the estimated age of the universe a property of the universe or of us as its observers?

Would a different observer perceive the age of the universe to be different? Do different parts of the universe have different ages? Do the principles of special relativity even apply when thinking on a universal scale?


texts: What is the composition of an asteroid in percentages?

texts:
I am developing a RPG game (or so I like to tell myself) within outer space. Within the game, players would be able to mine small asteroids and collect resources, in order to make money. I'm having some difficulty determining exactly how much of the resources there would be in relation to everything else gotten from the asteroid.

This image has provided me with a good idea of what asteroids generally contain. It does not, however, show me the quantities. For example, I'm fairly certain that an asteroid would have more oxygen than palladium, but I don't know by how much.

Question: Can someone tell me (or better yet show me) the percentage of materials within an asteroid? I realize not all asteroids are the same, so categorizing or averaging is fine. The more detailed the better. The ideal information would be a list of values that I can scale with asteroid size.


texts:
The Fox News article Arizona city played critical role in moon exploration history covers several interesting activities that took place in Arizona in preparation for the Apollo Moon landings.

It shows the telescope (shown below) and mentions that it was used to draw lunar maps.

There is more information about this telescope here and here as mentioned in this answer.

Question: Why does this Lowell Observatory telescope have so many knobs? What do they all do? Is it possible to identify the function of all of the annotated controls and devices on this complicated-looking telescope?

I've added some numbers to facilitate discussion. There is also a chain going between the locations of #4 and #5, though I don't know exactly what it couples.

click images for full size viewing

  above: Lowell Observatory telescope used by scientists who collaborated with artists to map out the moon for Apollo astronauts (Fox News) Source

below: Screenshot from July 9, 2019 Fox News video NASA lunar legacy in the Arizona desert


texts: Would a comet break up during a close pass of the Earth

texts: Would a short-period comet, with a 2-mile nucleus, be able to come within 200,000 miles of Earth without breaking up?


texts: How to calculate the position to be to see ISS passing in front of the moon or the sun?

texts:
I would like to know how to calculate the time/date of the ISS passing in front of the moon (between the observer and the moon) or the sun, or to calculate the position in which the observer have to be to see the ISS passing in front of the moon/sun.

Th goal is to make a photograph of the ISS in the moon/sun.

Is it possible with tools such as Stellarium?


texts:
I know that viewing Mercury is a challenge, but I'm fairly close to the equator and Mercury was at greatest elongation just a week ago.
In-the-sky.org says:

All around the world, Mercury is visible as an evening object, having recently passed greatest elongation east. From Taipei, however, it is not observable – it will reach its highest point in the sky during daytime and is no higher than 10° above the horizon at dusk.
12 Jul 2018, 12:00 CST   –  Mercury at greatest elongation east
27 Aug 2018, 05:48 CST   –  Mercury at greatest elongation west
06 Nov 2018, 22:59 CST   –  Mercury at greatest elongation east
15 Dec 2018, 23:17 CST   –  Mercury at greatest elongation west

Of course, since Mercury stays near the Sun it will always reach its highest point in the sky during daytime, probably around lunchtime!
But I don't understand why it would be viewable all around the world (presumably just after sunset since it is currently near maximum elongation East), but not from Taipei.
Question: Why does in-the-sky.org say that Mercury is not visible from Taipei these days?


texts: Which came first: Galaxies  Stars  Planets?

texts:
If a galaxy is defined as a collection of planetary systems (and all matter in between), and a planetary system is defined as a collection of planets circling a star (and all matter in between), and a planet (and other smaller bodies, like asteroids, moonlets, moons, etc) is basically just a very very, very large collection of minerals, stardust and gases (which make up the entire universe), which came first: The planets, planetary systems or galaxies? I've been given to understand the universe came first...but after that?

I thought I understood, at least the layman's basics, of the universe formation. However, today, I’m having trouble conceptualising the order in which they would have been formed, IF they are defined by the smaller unit.

Is this just me getting the semantics of classification and the actual chronology of each feature forming, mixed up?

VERY Basically,

The universe is made up of a complex mix of everything (matter, antimatter, darkmatter, to name just a few), and expanding 'space'.
A very, very, large area of 'space' is covered in very, very, tiny particles: made up of at first gases and later 'stardust'.
A galaxy is formed of gravity-attracted gases, and after the very first stars went supernova and exploded there was also 'stardust', which combines to create 'clumps' of interstellar clouds (cloud nebulae).
The cloud nebulae are the 'nursery' areas for star formation (both initial stars and later generation stars).
The newly created star uses remnants of 'stardust' in the cloud nebulae to form planetary systems and then, a 'short' time later the orbiting planets (and other sized objects).

So then the chronological order would be:

Universe (Largest scale) => gases (very small scale) => galaxy => interstellar clouds => stars => planets (combined to form planetary systems). And the tiny particles of gases and 'stardust', are involved in nearly all scales.

Image taken from spaceexplained

Just writing out this question has helped! I hope you don't mind me posting it anyway, as it might help others and I still need confirmation that I have, hopefully, worked myself out of my conundrum (not deeper).


texts: How can "Geysers" on Europa reach heights of 100km?

texts:
After seeing today's Washington Post's article NASA just saw Europa’s geysers erupting into space. Again., and especially the phrase "geysers erupting into space" I checked and Europa has a surface gravity of about 1.3 $m/s^2$, which is substantial - almost the same as the Moon's at about 1.6 $m/s^2$!

The BBC's website article Europa moon 'spewing water jets' says

  "Further evidence has been obtained to show that Jupiter's icy moon Europa throws jets of water out into space."

and

  "The suggestion is that the jets reach several hundred kilometres in height before then falling back on to Europa."

On earth, pressure can come from geological hydrostatic forces and by steam produced by geothermal heating, but they rarely rise beyond a few dozen meters. That would be perhaps 100 meters in Europa's gravity.

The images shown of the water above Europa show heights of 100 kilometers and more.

Unlike Earth rock being heavier than water, Europa's ice crust floats. What could be sources of hydrostatic pressure or pressurized steam near the surface that can create such "geysers" or "jets" that can project water to such heights in this gravity?

above:  The geyser Strokkur in Iceland, Earth, from here.


texts: When did the concept of "celestial sphere" fall?

texts:
I'm just done reading The Great Ptolemaic Smackdown, and it provided a good timeline of establishing heliocentrism, broad acceptation of Kepler's system, and the initial (failed) Galileo's experiment attempting measurement of parallax of distant stars (which was based on assumption of two near stars of different brightness being a long distance apart; Galileo unfortunately picked a binary star) - all the models described within assume a fixed, mostly immutable "celestial sphere" of distant stars.

When, and how was this concept disproven?


texts: Is it possible to calculate how much a star's brightness dims when a planet transits in front of it from a viewer's perspective?

texts:
Last night I got to thinking about what would happen if Jupiter and Venus suddenly switched places.

Since Venus comes the closest to Earth than any other planet and Jupiter is much larger, does that mean that Jupiter (now following the orbit of Venus) would appear large enough to eclipse the Sun from Earth's perspective?

Jupiter's angular diameter in this scenario is given by $$\delta = 2\arctan \left(\frac{d}{2D}\right)$$

where

$\delta$ is its angular diameter,
$d$ is its actual diameter,
$D$ is the distance between both bodies.

The closest Venus and Earth ever get to each other (in the near future) is $d = 39.5 \times 10^6$ km, and Jupiter's diameter is $D = 139,820$ km.

So if Jupiter replaced Venus, its maximum angular diameter would be $$\delta = 2\arctan \left(\frac{139,820}{2 \times 39.5 \times 10^6}\right)$$
$$\delta = 0.202812°, or \ 0° 12  ' 10.12 " $$

The Sun's angular diameter as seen from Earth is about 30 arcminutes, and so Jupiter in this scenario with only 12 arcminutes would not appear to be large enough to completely eclipse the Sun.

However, assuming it is a total transit, it would still cover $≈16.27 \%$ of the Sun's disk as seen from Earth. Surely that would result in a noticeable dim in the brightness of the Sun as seen from Earth, no?

Is there an equation to calculate how much a star's brightness dims when a planet transits in front of it from a viewer's perspective?


texts: Can Jupiter's nightside be classified as spectral type Y?

texts:
As far as I am aware, the latest spectral types that have been assigned are around Y2, for objects like WISE 0855-0714 that have temperatures around 250 K or so. I've also seen several directly-imaged exoplanets have had their spectra classified as L- or T-type (e.g. Bonnefoy et al. 2016 who find that the giant planets HR 8799 d and e are good matches for L6–L8 dwarfs).
Jupiter is colder and less massive than the observed Y dwarfs and differs from isolated brown dwarfs because it is being illuminated by the Sun, but there is thermal emission which could be observed from the nightside of the planet. Has Jupiter's nightside spectrum (i.e. the spectrum of Jupiter excluding contributions from reflected sunlight) been observed in sufficient detail to compare it to the spectra of Y dwarfs, and if so does it fit the trends observed in spectral type Y or is it so different that it cannot be spectrally classified as a Y dwarf?
For clarity: I am asking purely in terms of spectral classification, i.e. the classification of the spectrum. I am not asking about whether Jupiter is a brown dwarf making the Sun+Jupiter a binary system. That has been asked elsewhere.


texts: Does a White hole lies behind a Black hole?

texts:
While reading about a White holes, I stumbled upon a question "Where does the matter emitted by a White hole come from?" There seems to be 2 possible candidates:

It was the matter engulfed by a Black hole.
Matter was created inside the White hole.

My search on wiki stated that:

According to Penrose Diagram of Schwarzschild radius, objects first leave the White hole and then may enter into a Black hole. But, due to Hawking radiation, a Black hole can achieve thermal equilibrium with gas of radiation. This equilibrium state is reversal invariant, implying that time reversal of a Black hole is again a Black hole. This means that a Black hole and a White hole are same objects.

My 2nd candidate suggests that the big-bang was a white hole. I thought of ruling this out because it requires the existence of a white hole before the big-bang.

This forced me to draw the conclusion that a white hole must either be inside a black hole or behind it.

Is this correct (provided that we haven't yet proven the existence of a White hole)? Where am I wrong?


texts: How is the Hubble constant determined from gravitational waves?

texts:
We know there is a discrepancy between measurements of the Hubble constant, $H_0$. On one side there is the method of the Planck mission, where they use the CMB and the $\Lambda$CDM model to determine the Hubble constant. On the other side, they use standard candles, like Cepheid variables (for example: Riess et al., 2019) and red giants (for example: Freedman et al., 2020). The very precise measurements don’t overlap and thus we need a ‘solution’.

One way to improve our knowledge about $H_0$ is by using gravitational waves to determine the Hubble constant (Feeney et al., Arxiv version). They compare the measured ‘strength’ of the gravitational wave with the ‘strength’ of the wave when it was created to determine the distance to the source object. But how do they calculate/determine the ‘strength’ of the wave at the source? I know they also use an EMS observation for calculating the redshift (and that redshift converted to radial velocity divided by the distance gives $H_0$), but from where do they calculate the source-‘strength’ of the gravitational wave? How can they otherwise determine how much energy the wave has lost? I can’t seem to find the answer.